1. Field of the Invention
The present invention relates to an oxo-titanylphthalocyanine crystal formed from an oxo-titanylphthalocyanine compound, a method for producing the oxo-titanylphthalocyanine crystal, and an electrophotographic photoreceptor. In particular, the invention relates to an oxo-titanylphthalocyanine crystal which is stable, is superior in dispersibility in a photoreceptive layer and efficiently contributes to improvements in sensitivity and charge retention rate in en electrophotographic photoreceptor, a method for producing the oxo-titanylphthalocyanine crystal, and an electrophotographic photoreceptor.
2. Description of the Related Art
Generally, as electrophotographic photoreceptors for use in electrophotographic devices such as copying machines and laser printers, many organic photoreceptors have been used to cope with, for example, demands for low costs and a resistance to environmental pollution. As charge generating agents for use in such organic photoreceptors, widely used are phthalocyanine type pigments sensitive to infrared or near-infrared light emitted from a semiconductor laser, infrared LED or the like.
Also, it is known that such phthalocyanine type pigments include non-metal phthalocyanine compounds, copper phthalocyanine compounds, titanylphthalocyanine compounds and the like depending on their chemical structures, and also, each phthalocyanine compound can take various crystal forms by a difference in production conditions.
It is known that when an electrophotographic photoreceptor using oxo-titanylphthalocyanine compound having a Y-type crystal structure as the charge generating agent is produced in the presence of many types of phthalocyanine compound crystals differing in crystal type, electric characteristics in the electrophotographic photoreceptor are more improved as compared with the case of using oxo-titanylphthalocyanine having other crystal types.
With regard to the Y-type oxo-titanylphthalocyanine crystal, a method for producing an oxo-titanylphthalocyanine crystal having a maximum diffraction peak at a Bragg angle (2θ±0.2°)=27.3° with respect to CuKα ray in an X-ray diffraction spectrum is disclosed, wherein an organic compound capable of forming a phthalocyanine ring and a titanium compound are made to react with each other at 130° C. for about 4 hours in dialkylamino alcohol to which urea or ammonia is added (for example, refer to the following patent document 1).
Also, a method for producing an oxo-titanylphthalocyanine crystal is disclosed in which o-phthalonitrile is made to react directly with titanium tetrabutoxide without using a urea compound at 215° C. for about 2 hours (for example, refer to the following patent documents 2 and 3).
More specifically, disclosed is a method for producing an oxo-titanylphthalocyanine crystal having a peak in a predetermined range in a CuKα characteristic X-ray diffraction spectrum and no temperature variation peak in a temperature range from 50 to 400° C. in differential scanning calorimetric analysis.
However, in the case of the patent document 1, the addition proportion of the titanium compound to the organic compound capable of forming a phthalocyanine ring is small whereas the addition proportion of urea and the like to the organic compound capable of forming a phthalocyanine ring is excessive and also, reaction temperature is low. There is therefore the problem that produced Y-type oxo-titanylphthalocyanine crystals tend to undergo crystal transition into β-type or α-type crystals in a photoreceptive layer application liquid. For this reason, the photoreceptive layer application liquid is deteriorated in storage stability, with the result that there is the problem that no photoreceptive layer having good electric properties can be stably formed.
On the other hand, in the case of using the oxo-titanylphthalocyanine crystals described in the patent documents 2 and 3, there is a problem concerning low dispersibility in a photoreceptive layer though the crystal transition in the photoreceptive layer application liquid can be suppressed to some extent. As a result, there are problems concerning reduced sensitivity and reduced charge retention rate in electrophotographic photoreceptors using the oxo-titanylphthalocyanine crystals as charge generating agents.    [Patent document 1] JP-A H08-176456 (examples)    [Patent document 2] JP 3463032 (claims)    [Patent document 3] JP-A 2004-145284 (claims)